The invention relates to a system for reproduction machine control, and more particularly, to a technique for the maintenance and recovery from an NVM (non-volatile memory) data integrity failure for such reproduction machines.
As reproduction machines such as copiers and printers become more complex and versatile in executing job requirements, the importance of permanently maintaining a wide range of data such as processing conditions and fault history, customer data, and job related information becomes even more critical for production efficiency and record keeping. It is customary to store critical information in non-volatile memory (NVM) as a precaution against information loss due to power loss and machine shutdown. However, due to such factors as electrical noise and the failure of the NVM itself, there is always the potential of losing vital NVM data.
In the prior art there are examples of non-volatile memories and attempts to maintain permanent data. For example:
U.S. Pat. No. 4,393,500 to Imazeki et al. discloses a method of modifying data stored in non-volatile memory wherein a binary 1 is written into an area of the non-volatile memory and can be checked later to see if any problems occurred. See col. 4, lines 27-31. A bubble memory is used as a non-volatile memory.
U.S. Pat. No. 4,584,663 to Tanikawa discloses an apparatus for a power-on data integrity check for volatile memory, but a similar method can also be used for non-volatile memory. See col. 4, lines 44-46. A means is provided to test a memory using another copy of the same contents as that memory. See col. 3,lines 50-55.
U.S. Pat. No. 4,458,349 to Aichelmann, Jr. et al. discloses a method of storing data words in fault tolerant memory in which a check byte is stored with a data word (see col. 4, lines 18-22) and can then later be checked. See col 4, lines 27-30. A means is also provided to correct single bit errors.
U.S. Pat. No. 4,698,808 to Ishii discloses a method of detecting intermittent errors in volatile memory in which a checksum is used to test a memory. See col. 2, lines 23-29. A means is also provided to copy over corrupted data with fresh data. See col. 3,lines 10-12.
U.S. Pat. No. 4,819,237 to Hamilton et al. discloses a method for monitoring the validity of volatile memory in which a bit pattern is used to detect corruption in a memory. See col. 2, lines 41-49. A means is provided to check this pattern later against a copy which resides in non-volatile memory.
A difficulty with the prior art machine systems is the difficulty in maintaining status and restoring a machine to the proper parameters during operation. It would be desirable to be able to provide a simple and relatively inexpensive method to save and restore machine parameters. Another difficulty with the prior art is the relatively complex and time consuming operation that is required to transfer NVM data to a mass storage memory and also the susceptibility of a non-volatile memory to real time malfunctions.
It is an object, therefore, of the present invention to provide a method to automatically check the integrity of a non-volatile memory in real time and to be able automatically to save and restore non-volatile memory data. Other advantages of the present invention will become apparent as the following description proceeds, and the features characterizing the invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.